Constant flow rate burette

ABSTRACT

A burette assembly for discharging liquids at a constant flow rate regardless of the height of solution in the burette. This result is accomplished by attaching a capillary tube to the wall of a conventional burette. The tube is vented to the atmosphere at one end and terminates at the other end at a point on the inside of the bottom portion of the barrel of the burette.

[ 1 memos United States Patent 3,145,876 8/1964McBrien....................... 222/158 X [72] lnventor Hardy C. CroomValdosta,Ga.

m 9 51L. 8 m. 3mm SI Pw 3u 8 0 0. de N mm L Hg wmmn Ha AFPA 1:11] 2532247 [1.11.

Attornjeys-David R. Birchall and E. J. Holler [54] CONSTANT FLOW RATEBURETTE 5 Claims, 2 Drawing Figs.

A burette assembly for discharging liquids at a constant flow rateregardless of the height of solution in the A 9 3 SUNS 2 12 lz 3 3 2 2 uI e "3 a" m m N m mh n "c n "M q I; S HM k U hF H m U 55 292; 222/158;73/426 burette. This result is accomplished by attaching a capillarytube to the wall of a conventional burette. The tube is ventedReferences Cited UNITED STATES PATENTS 8/1937 l-lopfet a1.

to the atmosphere at one end and terminates at the other end at a pointon the inside of the bottom portion of the barrel the burette.

PATENTED SEP21 I971 INVENTOR.

HARD Q.C.m FlG l Hafiz/3M QEYS PUT oil.

CONSTANT FLOW RATE BURE'I'IE THE INVENTION This invention relates to aburette assembly, and more particularly, the invention relates to aburette which will discl. .rge a quantity of liquid at a constant flowrate independent of the height of the liquid in the burette.

The common titration operation in performing volumetric and quantitativeanalysis involves the measurement of the amount of a standard reagentsolution, one of known strength, required for reaction with a samplesolution of known volume, but unknown strength. This operation iscarried out with a burette comprising a long transparent cylinder ofuniform bore for measuring the volume of standard solutions deliveredtherefrom.

I-Ieretofore, burettes were designed to improve the accuracy andefficiency of the titration operation. To this end, burette constructionincluded means to fill the barrel through attached funnels, means topressure fill the burette, means to prevent evaporation of the liquidfrom storage reservoirs into the atmosphere, means to prevent stopcocksfrom sticking or leaking, means to make barrel graduations easy to read,means to prevent contamination of the stored liquid and means to releasea predetermined volume of liquid. None of these burettes, however, havebeen constructed to discharge liquid at a constant flow rate.

Therefore, the primary object of this invention is to provide a burettefor discharging liquid at a constant rate of flow.

An object of this invention is to provide a venting tube attached to thebarrel of the burette, the upper end of which is vented to theatmosphere and the lower of which opens into the lower portion of thebarrel of the burette.

Another object of this invention is to more accurately control the rateof flow of discharging liquid through the combination of a draw and fillstopcock and a separate rate of flow stopcock.

Another object of this invention is to provide a burette which may beconnected to a pH meter or a millivoltrneter with a recording chart sothat the amount of liquid discharged from the burette may be readdirectly from the chart.

An object of this invention is to provide a burette in which the rate ofdischarge can be adjusted to deliver a definite volume of liquid perscale division on the recorder chart independent of the height of theliquid in the burette.

Other objects and features of the advantages of the present inventionwill be found throughout the following description of the invention,particularly when considered with the accompanying drawings.

IN THE DRAWING FIG. 1 of the drawings is a partial sectional view of theconstant flow burette.

FIG. 2 is a partial sectional view of the venting stopcock of theconstant flow burette in the open position.

FIG. 1 of the drawings shows a burette made of glass or othertransparent material with a barrel or cylindrical portion 11 of auniform bore. Barrel 11 has imposed on the surface thereof uniformlypositioned graduation lines 12 which are divided into a flow stabilitysection 15 located above zero point 16 and a titration section 17located below zero point 16.

Burette 10 contains an overflow funnel 20 integrally connected to thetop portion of barrel 11. Immediately below the attached funnel, thereis a venting stopcock 23 provided with passages 26 and 27 which areperpendicular to each other.

FIG. 2 of the drawings shows the position of stopcock 23 with capillarytube 34 vented to the atmosphere. In this position, passage 26 isaxially aligned with the portions of capillary tube 34 above and belowstopcock 23, while passage 27 is in the off position.

Referring to FIG. I. capillary tube 34 with an internal diameter in therange of 0.01 to 0.40 inches is positioned along the wall of barrel IIand funnel 20 and extends downwardly to a point in.the bottom portion ofthe burette just'above the opening 39 leading to discharge tip 37. Theheight of the capillary tube 34 extending upwardly along the wall ofbarrel 11 should be greater than the height of the liquid in the barrel.Therefore, capillary tube 34 extends upwardly to a point along the wallof barrel 11 above venting stopcock 23.

In the preferred embodiment of this burette, capillary tube 34 ispositioned outside of barrel 11. It is attached to the wall of barrel 11at various points along the wall. Capillary tube 34 enters into thebottom portion of the barrel just above opening 39 leading to dischargetip 37 and extends upwardly within the barrel to facilitate the smoothemission of bubbles through the liquid in the burette. If capillary tube34 has a very small inside diameter, then small bubbles are permitted torise to the surface of the liquid in the burette, and the surface of theliquid is not constantly ajarred as it would be if large bubbles rose tothe surface. The upper portion of capillary tube 34 is connected topassage 26, in stopcock 23. A portion of tube 34 extends above stopcock23 and communicates with the portion below said stopcock 23 throughpassage 26, when passage 26 is in the open position.

The lower portion of burette 10 contains a fill and draw stopcock 24.Angularly disposed passages 29 and 30 of stopcock 24 respectivelycommunicate between opening 39 and discharge tip 37 and tip 38. A rateof flow stopcock 25 with passage 31 is positioned within discharge tip37 to control the flow rate of the emanating liquid.

The operation .of the burette is as follows:

The burette 10 would be filled in the conventional manner through tip 38which is connected to a supply of standard solution. During the fillingprocess, stopcock 23 is opened to the air through passage 27 whilepassage 26 is in the closed position. This allows capillary tube 34 tofill partially with liquid. Stopcock 25 is also turned to the closedposition during filling. After the burette is filled, with any overflowaccumulating in funnel 20, stopcock 24 is rotated approximately to theclosed position so that passage 30 no longer communicates betweenopening 39 and tip 38. Stopcock 23 is then turned approximately 90 asshown in FIG. 2 so that passage 26 is in an open position communicatingbetween the portions of capillary tube 34 above and below the stopcock.Passage 27 is now in a closed position. A column of entrapped air isthereby formed between the liquid level in the burette and the closedpassage 27. Stopcock 24 is rotated approximately 90 to cause dischargethrough passage 29. A waste discharge receptacle containing a pH meterelectrode or a millivoltmeter electrode connected to a recording chartis placed below discharge tip 37. When the rate of flow stopcock 25 isturned to the discharge position, liquid begins to exit tip 37. With therecording chart running, the rate of flow of discharging liquid isadjusted by means of stopcock 25 to deliver a definite volume of liquidper scale division on the recording chart, using the liquid in the upperflow stabilizing section 15 of the burette to adjust the flow.

The pressure exerted on the top of the liquid column in the burette bythe entrapped column of air above the liquid is decreased while theliquid is discharging to a point where the pressure at the base 33 ofthe capillary tube 34 created by the sum of the atmospheric pressureexerted on the liquid in the capillary tube and the pressure exerted onthe base 33 of the capillary tube by the liquid itself in the tube isgreater than the pressure exerted on the base 33 of capillary tube 34created by the sum of the pressure exerted by the trapped column of airon the liquid in barrel ll of the burette and the pressure exerted onthe base 33 of the capillary tube 34 by the liquid in the barrel of theburette. At that point, the height of liquid in capillary tube 34rapidly decreases with respect to the height of liquid in barrel 1] ofthe burette. Finally, the tube is absent of liquid, and air begins tobubble through the tube, through the liquid in barrel ll of the buretteand up to the cylinder of entrapped air. When these bubbles begin toform within the liquid, the pressure at the base 33 of capillary tube 34is equal to that of the atmosphere.

By making the diameter of the capillary tube very small with respect tothe diameter of the burette, the liquid in the tube is quicklydischarged until air bubbles begin to form at base 33 of the tube. Solong as the height of the liquid in the burette is above that of base 33of the capillary tube, air bubbles will displace the discharging liquid,and the liquid will flow from the burette at a constant rate.

After the rate of flow stopcock 25 is adjusted to deliver I milliliterof liquid or any other desired volume of liquid per scale division onthe recorded chart and the liquid level within barrel 11 is made tocoincide with zero point 16, fill and draw stopcock 24 is rotated tostop discharge. There should be no liquid in capillary tube 34 at thispoint, and the pressure at the datum of tip 33 will be that of theatmosphere.

The solution to be titrated is placed under discharge tip 37. Stopcock24 is turned to direct liquid through discharge tip 37 at the same timea chart division on the recorded chart is under the recorder pen. If therate of flow from discharge tip 37 has been properly adjusted,subsequent chart divisions will pass under the pen on the recordingchart as the liquid level in the barrel of the burette passes eachmilliliter graduation.

If the end point of the titration in pH or millivolts is known, nofurther attention is necessary, and the end point of the analysis inmilliliter titrated can be read directly from the recorder chart.

The following explanation is set forth to show how applicant believesthe burette yields a discharge flow rate which is constant.

Definitions P, Pressure exerted at the bottom of discharge tip 37 by thecolumn of entrapped air in the burette and the liquid in the burette.

P,,,, Pressure exerted by the entrapped air within burette upon theliquid in the burette.

P, Pressure exerted at the base 33 of the capillary tube by the liquidin the burette.

P, Pressure exerted at the base 3.) of the capillary tube from thecolumn of entrapped air and the liquid in the burette.

P Pressure of the atmosphere.

H Height of solution between the end of the discharge tip 37 and thebase 33 of capillary tube 34.

r= Rate of flow at which liquid is emanating from discharge tip 37.

FDensity of liquid within the burette.

The relationship between r, the rate of which liquid is leaving thedischarge tip 37, and p,, the total pressure at the bottom of the tip,is such that when p, is constant, the rate of discharge r from the tipis also constant. Therefore, if it can be shown that the pressure p, atthe tip of the burette is constant, then the rate of flow, r, from theburette will also be constant.

The pressure P exerted at the bottom of the capillary tube by the airand liquid in the burette is the sum of the pressure exerted by thecolumn of displaced air in the burette, P,,,,, and the liquid above thebottom of the capillary tube, P,.

When the burette is operated in the conventional manner, there is noliquid in the capillary tube. As liquid is discharged from the burette,tiny bubbles of air pass from the bottom of the capillary tube throughthe liquid in the barrel of the burette and then diffuse into the aircolumn above the liquid in the burette. Therefore, the pressure at thebottom of the capillary tube must be equal to atmospheric pressure,since there is no liquid in the tube. (2) P, P,,,,,,

But for the short length of time necessary to perform a titrationoperation, P,,,,,, is constant. (3) P,,,,, K

Now, substituting equation (3) back into equation (2), (4)

The pressure P, at the bottom of discharge tip 37 is determined from thesummation of the pressure P,,,, exerted by the entrapped air, thepressure P exerted by the column of liquid above the base of thecapillary tube, and the pressure of the column of liquid between thedischarge tip and the base of the ca ill tube.

in e the pressure exerted by the liquid column between the discharge tipand the bottom of the capillary tube is determined by the density of theliquid and its height,

Substituting equation l into equation (5 But from equation (4), P, K,.

Therefore, (6) becomes Since both 6, the liquid density, and H, theheight of solution between the end of the discharge tip and the bottomof the capillary tube are constants, then Since P, is constant, the rateof discharge, r, from the burette is also constant.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will become apparent tothose skilled in this art that various changes and modifications may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. An apparatus for discharging liquid at a constant flow ratecomprising in combination:

a. a reservoir for holding a quantity of liquid to be discharged,

a first stopcock connected to the bottom portion of said reservoir andhaving a transverse passage therethrough to permit the discharge ofliquid from said reservoir,

0. means connected to the top portion of said reservoir to vent theliquid in the reservoir to the atmosphere during filling and to closethe top portion of the reservoir from the atmosphere during discharge,

d. a capillary tube open at both ends attached to said reservoir andextending in an upward direction to a point above the upper end of saidreservoir, and

e. the upper end of said capillary tube having means for closing saidtube from the atmosphere during filling of the reservoir and the lowerend opening into the lower portion of said reservoir above the stopcock,thereby permitting said reservoir to discharge liquid at a constant flowrate.

2. The apparatus as claimed in claim 1, wherein said reservoir comprisesa tube having graduations thereon indicating the volume of liquiddischarged.

3. The apparatus as claimed in claim 1, including a second stopcockpositioned below said first stopcock and integrally connected to adischarge tip that is in turn connected to said first stopcock, saidsecond stopcock having a transverse passage therethrough, therebycontrolling the rate of discharge of liquid from the discharge tip.

4. The apparatus as claimed in claim 1 wherein the lower end of saidcapillary tube is U-shaped and is positioned within said reservoir sothat the opening of said capillary tube is within said reservoir and isdirected toward the top portion of the reservoir 5. The apparatus asclaimed in claim 1, including:

a. a funnel connected to said reservoir for storing liquid,

b. a third stopcock connected integrally to the funnel, the

reservoir and the capillary tube, said third stopcock containingpassages for directing liquid into said funnel and for venting saidcapillary tube to the atmosphere.

2. The apparatus as claimed in claim 1, wherein said reservoir comprisesa tube having graduations thereon indicating the volume of liquiddischarged.
 3. The apparatus as claimed in claim 1, including a secondstopcock positioned below said first stopcock and integrally connectedto a discharge tip that is in turn connected to said first stopcock,said second stopcock having a transverse passage therethrough, therebycontrolling the rate of discharge of liquid from the discharge tip. 4.The apparatus as claimed in claim 1 wherein the lower end of saidcapillary tube is U-shaped and is positioned within said reservoir sothat the opening of said capillary tube is within said reservoir and isdirected toward the top portion of the reservoir .
 5. The apparatus asclaimed in claim 1, including: a. a funnel connected to said reservoirfor storing liquid, b. a third stopcock connected integrally to thefunnel, the reservoir and the capillary tube, said third stopcockcontaining passages for directing liquid into said funnel and forventing said capillary tube to the atmosphere.